BEIRUT -- A "huge explosion" Thursday in northern Syria leveled a hotel that government troops used as a military base, along with several other buildings in a government-held area, state television and activists reported.

Syrian state television said the explosion struck on the edge of a contested old neighborhood in Aleppo. The television report identified the hotel as the Carlton hotel, located next to the city's ancient Citadel.

A local activist group called the Sham News Network also reported the blast, saying that President Bashar Assad's troops were based in the hotel.

Another activist group, the Britain-based Syrian Observatory for Human Rights, said the explosion struck a government-held district in Aleppo's Old City, next to rebel positions. The Observatory said the rebels belonging to the Islamic Front -- an umbrella group of Islamic militant factions based in northern Syria -- planted a huge amount of explosives in a tunnel they dug below the Carlton hotel, detonating it remotely.

It said the hotel was completely destroyed in the blast and that there were casualties among the troops.

The attack on the Carlton was the second allegedly carried out by militants using explosives-packed tunnels this year.

In February, CBS News' Khaled Wassef reported that the Islamic Front had released a video showing militants digging tunnels under the Carlton Hotel. They claimed it took them three months to dig the tunnel. On Feb. 16, they carried out a bombing that caused significant damage to the building, but failed to knock it down completely.

An image taken from video posted online in February, 2014 by the Syrian rebel group Islamic Front shows a militant in a tunnel allegeldy dug by the group underneath the Carlton Hotel in Aleppo.

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Aleppo, the country's largest city and former commercial hub, is carved up into rebel-held and government-held areas since the rebels launched an offensive there in mid-2010, capturing territory along Syria's northern border with Turkey.

In recent months, government aircraft relentlessly has bombed rebel-held areas of the city and the opposition fighters have hit back, firing mortars into government-held areas. The rebels also have detonated car bombs in residential areas, killing dozens of people.

Meanwhile, more rebels are expected to leave the central city of Homs, as the evacuation of opposition fighters moves into its second day. Hom is Syria's third largest city that was known as "the capital of anti-Assad revolution" since the uprising against his rule erupted started in March 2011.

Homs Gov. Talal Barazi told Syrian state TV late Wednesday that that the evacuation process is being conducted in "positive atmosphere." He said Homs will be declared a "secure" city once the army moves in later Thursday.

The Observatory, which has been documenting Syria's 3-year-old conflict through a network of activists on the ground, said that about 250 opposition fighters remain in the old districts of Homs, where they have been holed up under a crippling government siege for more than two years. The Obesrvatory's head, Rami Abdurrahman, said more than 960 left the city Wednesday.

In exchange for the rebels' safe departure from Homs, the opposition fighters have released 70 people who had been held by gunmen in various areas, including in Aleppo and in the costal province of Latakia, Barazi said. Among those released were 17 women and five children, he said.

Syria's uprising began with largely peaceful protests and has evolved into a civil war with sectarian overtones, pitting largely Sunni Muslim rebels against Assad's government that is dominated by Alawites, a sect of Shiite Islam.

Islamic extremists, including foreign fighters and Syrian rebels who have taken up hard-line al Qaeda-style ideologies, have played an increasingly prominent role among fighters, dampening the West's support for the rebellion to overthrow Assad.